(1) Field of the Invention
The present invention relates a process and an apparatus for treating an exhaust gas through capturing and disposing of particulates composed mainly of carbon in exhaust gases discharged from engines such as diesel engines, and also to a honeycomb structural exhaust gas filters adapted to capture such particles and allow them to be removed with a gas stream that flows in a direction reverse to that of the exhaust gas flow.
(2) Related Art Statement
Particulates composed mainly of carbon are contained at a high concentration in exhaust gases from the diesel engines, which causes pollution. Various proposals have been made on exhaust gas filters to capture and remove such particulates in the exhaust gases.
For example, according to unexamined Japanese patent application Laid-open No. 1-159,408 discloses a technique in which carbonaceous particulates are captured by a honeycomb structural filter, the captured particulates are removed from inner walls of the filter with a back-washing gas stream intermittently flown in a direction reverse to that of passing the exhaust gas through the filter, and the removed particulates are burnt in a recapturing section provided inside the exhaust gas flow passage upstream near the filter. In the above honeycomb structural filter, given gas flow holes are closed at one end of the honeycomb structure, and the remaining gas flow holes are closed at the other end.
However, there is a fear that since the recapturing section is provided in the exhaust gas flow passage under or near the filter, the particulates peeled by back wash gas stream are blown back to the filter again without being caught in the recapturing section.
Further, in such a conventional honeycomb structural filter as the exhaust gas filter, when particulates caught by the exhaust gas filter are to be peeled off with a back wash gas stream, the back wash gas stream is difficult to flow near the sealed portions of the gas flow holes on the upstream side of the back wash gas stream. Consequently, the particulates heaped in the filter are not fully peeled off and partially remain. Thus, the exhaust gas filter is not fully regenerated, which causes increase in the pressure loss of the filter.